U.S. patent application number 11/439847 was filed with the patent office on 2007-11-29 for methods for enhancing resolution of a chemically amplified photoresist.
Invention is credited to Bruno LaFontaine, Adam R. Pawloski, Thomas Wallow.
Application Number | 20070275321 11/439847 |
Document ID | / |
Family ID | 38749932 |
Filed Date | 2007-11-29 |
United States Patent
Application |
20070275321 |
Kind Code |
A1 |
LaFontaine; Bruno ; et
al. |
November 29, 2007 |
Methods for enhancing resolution of a chemically amplified
photoresist
Abstract
Methods are provided for enhancing resolution of a chemically
amplified photoresist. A film comprising a photoacid generator and
a polymer comprising functional groups bonded to protecting
moieties is deposited on a substrate. The film is exposed to
patterned radiation. The patterned radiation results in protonation
of a portion of the functional groups and the formation of a latent
image within the film. The bonds between the protonated functional
groups and the protecting moieties are selectively excited with
non-thermal energy having a wavelength spectrum that resonantly
cleaves the bonds.
Inventors: |
LaFontaine; Bruno;
(Pleasanton, CA) ; Pawloski; Adam R.; (San Jose,
CA) ; Wallow; Thomas; (San Carlos, CA) |
Correspondence
Address: |
INGRASSIA FISHER & LORENZ, P.C. (AMD)
7150 E. CAMELBACK ROAD, SUITE 325
SCOTTSDALE
AZ
85251
US
|
Family ID: |
38749932 |
Appl. No.: |
11/439847 |
Filed: |
May 24, 2006 |
Current U.S.
Class: |
430/270.1 |
Current CPC
Class: |
G03F 7/0382 20130101;
G03F 7/0392 20130101; G03F 7/2022 20130101; Y10S 430/145 20130101;
Y10S 430/146 20130101 |
Class at
Publication: |
430/270.1 |
International
Class: |
G03C 1/00 20060101
G03C001/00 |
Claims
1. A method for enhancing resolution of a chemically amplified
photoresist, the method comprising the steps of: depositing on a
substrate a film comprising a photoacid generator and a polymer
comprising functional groups bonded to protecting moieties;
exposing the film to patterned radiation, wherein the patterned
radiation results in protonation of a portion of the functional
groups and the formation of a latent image within the film; and
selectively exciting the bonds between the protonated functional
groups and the protecting moieties with non-thermal energy having a
wavelength spectrum that resonantly cleaves the bonds.
2. The method of claim 1, wherein the step of selectively exciting
the bonds between the protonated functional groups and the
protecting moieties with non-thermal energy having a wavelength
spectrum that resonantly cleaves the bonds comprises the step of
exciting the bonds with non-thermal energy having a wavelength
spectrum narrower than that of black body radiation.
3. The method of claim 2, wherein the step of selectively exciting
the bonds between the protonated functional groups and the
protecting moieties with non-thermal energy having a wavelength
spectrum that resonantly cleaves the bonds comprises the step of
exciting the bonds with non-thermal energy having a wavelength
spectrum that corresponds to the absorption spectrum of the
bonds.
4. The method of claim 1, wherein the step of selectively exciting
the bonds between the protonated functional groups and the
protecting moieties with non-thermal energy comprises the step of
selectively exciting the bonds with infrared radiation, radiation
having a wavenumber of 1750 cm.sup.-1, radiation having a
wavenumber of 1180 cm.sup.-1, or microwave radiation.
5. The method of claim 1, further comprising the step of applying
heat to the film after the step of exposing the film to patterned
radiation.
6. The method of claim 1, further comprising the step of cooling
the film after the step of exposing the film to patterned
radiation.
7. The method of claim 1, further comprising the step of heating
the film before the step of exposing the film to patterned
radiation.
8. The method of claim 1, wherein the step of selectively exciting
the bonds between the protonated functional groups and the
protecting moieties with non-thermal energy comprises the step of
continuously exposing the film to the non-thermal energy.
9. The method of claim 1, wherein the step of selectively exciting
the bonds between the protonated functional groups and the
protecting moieties with non-thermal energy comprises the step of
exposing the film to pulses of the non-thermal energy.
10. The method of claim 1, wherein the step of selectively exciting
the bonds between the protonated functional groups and the
protecting moieties with non-thermal energy comprises the step of
exposing the film to the non-thermal energy for a period of about 2
seconds to about 5 minutes.
11. The method of claim 1, wherein the step of depositing on a
substrate a film comprising a photoacid generator and a polymer
comprising functional groups bonded to protecting moieties
comprises the step of depositing on a substrate a film comprising a
photoacid generator and a polymer comprising functional groups
bonded to acid labile groups.
12. A method for generating a resist image on a substrate, the
method comprising the steps of: coating a substrate with a
chemically amplified photoresist comprising a photoacid generator
and a polymer having functional groups bonded to acid labile
groups; generating acid from the photoacid generator and effecting
protonation of a portion of the functional groups of the polymer by
the acid; and exposing the chemically amplified photoresist to
electromagnetic radiation having a wavelength spectrum that is
narrower than that of black body radiation and that corresponds to
the absorption spectrum of the bonds between the protonated
functional groups and the acid labile groups.
13. The method of claim 12, further comprising the step of
contacting the chemically amplified photoresist with a developer
after the step of exposing the chemically amplified photoresist to
electromagnetic radiation.
14. The method of claim 12, wherein the step of generating acid
from the photoacid generator and effecting protonation of a portion
of the functional groups of the polymer comprises the step of
exposing the chemically amplified photoresist to patterned
radiation.
15. The method of claim 14, wherein the step of exposing the
chemically amplified photoresist to patterned radiation comprises
the step of exposing the film to patterned x-ray radiation,
patterned e-beam radiation, patterned ion beam radiation, patterned
EUV radiation, or patterned ultraviolet radiation.
16. The method of claim 12, wherein the step of exposing the
chemically amplified photoresist to electromagnetic radiation
comprises the step of exposing the chemically amplified photoresist
to infrared radiation, radiation having a wavenumber of 1750
cm.sup.-1, radiation having a wavenumber of 1180 cm.sup.-1, or
microwave radiation.
17. The method of claim 12, further comprising the step of applying
heat to the film after the step of generating acid from the
photoacid generator and effecting protonation of a portion of the
functional groups of the polymer.
18. The method of claim 12, further comprising the step of cooling
the film after the step of generating acid from the photoacid
generator and effecting protonation of a portion of the functional
groups of the polymer.
19. The method of claim 12, wherein the step of exposing the
chemically amplified photoresist to electromagnetic radiation
comprises the step of exposing the film to pulses of
electromagnetic radiation.
20. A method for device fabrication comprising the steps of:
forming a layer of chemically amplified photoresist on a substrate,
wherein the chemically amplified photoresist comprises a photoacid
generator and a polymer having bonds between functional groups and
protecting groups; exposing the layer of chemically amplified
photoresist to patterned radiation selected from the group
consisting of ultraviolet radiation, EUV radiation, x-ray
radiation, electron beam radiation, and ion beam radiation to
introduce an image into the photoresist; effecting protonation of
the functional groups; subjecting the layer of chemically amplified
photoresist to electromagnetic radiation that has a wavelength
spectrum that corresponds to the absorption spectrum of the bonds
such that the protecting groups are disassociated from the
protonated functional groups; developing the image into a pattern;
and transferring the pattern into the substrate.
21. The method of claim 20, wherein the step of effecting
protonation of the functional groups results from the step of
exposing the layer of chemically amplified photoresist to patterned
radiation.
22. The method of claim 20, wherein the step of subjecting the
layer of chemically amplified photoresist to electromagnetic
radiation comprises the step of subjecting the chemically amplified
photoresist to infrared radiation, radiation having a wavenumber of
1750 cm.sup.-1, radiation having a wavenumber of 1180 cm.sup.-1, or
microwave radiation.
23. The method of claim 20, further comprising the step of applying
heat to the chemically amplified photoresist after the step of
effecting protonation of the functional groups.
24. The method of claim 20, further comprising the step of cooling
the film after the step of effecting protonation of the functional
groups.
25. The method of claim 20, wherein the step of subjecting the
layer of chemically amplified photoresist to electromagnetic
radiation comprises the step of subjecting the layer of chemically
amplified photoresist to pulses of electromagnetic radiation.
Description
FIELD OF THE INVENTION
[0001] The present invention generally to photolithography, and
more particularly relates to methods for enhancing resolution of
chemically amplified photoresists.
BACKGROUND OF THE INVENTION
[0002] Devices such as integrated circuits are complex structures
made of a variety of materials. They are fabricated from the
sequential formation of alternating and interconnecting bands of
conductive, semiconductive and nonconductive layers on an
appropriate substrate (e.g., silicon wafer) that are selectively
patterned to form circuits and interconnections to produce specific
electrical functions.
[0003] Photolithography is a commonly practiced process of creating
a patterned mask on the surface of a semiconductor wafer so that
subsequent patterned processes may be performed. Typically these
subsequent patterned processes involve the addition or subtraction
of a material by deposition, implant doping, or plasma etching.
[0004] Frequently, the pattern is transferred from an exposure mask
to the wafer using a photoresist layer and optical lithography
exposure tools. A positive or negative image of the desired
configuration is first introduced into the resist by exposing it to
patterned radiation which induces a chemical change in the exposed
portions of the resist. This chemical change is then exploited to
develop a pattern in the resist, termed a "latent image." This
pattern is then transferred into the substrate underlying the
resist.
[0005] A variety of resist materials are employed in lithographic
processes for device fabrication. One class of such resist
materials includes chemically amplified photoresists. A chemically
amplified photoresist is a photoresist to which an acid catalyst
reaction is applied. The resist contains a polymer that has certain
functional groups, for example, alcohol (OH), phenol
(C.sub.2H.sub.5OH), carboxylic acid (COOH), and the like. A certain
portion of these functional groups are "masked", i.e., the hydrogen
atom is removed and replaced by moieties referred to as protecting
groups. These protecting groups are removable from the polymer by
acidolysis or hydrolysis.
[0006] The resist materials also contain an energy-sensitive
material in combination with the polymer. When exposed to a certain
energy (energy of a particular wavelength) or type (i.e., electron
beam), a moiety is generated from the energy-sensitive material
which effects the cleavage of the protecting group, thereby
"unmasking" the functional group in a "deprotection" reaction. When
the protecting group is an acid labile group, i.e., it is removed
in the presence of acid, the energy sensitive material is typically
a photoacid generator (PAG). The greater the number of protecting
groups that are cleaved from the polymer, the greater the chemical
contrast between the polymer exposed to radiation and the polymer
not exposed to radiation. This chemical contrast between the
unexposed resist material and the exposed resist material is
exploited to develop a pattern in the resist material.
[0007] The chemical contrast is typically a difference between the
solubility of the exposed resist compared to that of the unexposed
resist in a developer solution, which is typically an aqueous
alkali solution. In the case of positive resists, for example,
those areas of the photoresist that were not exposed to activating
radiation are generally not soluble in alkali, thereby providing a
dissolution differential between exposed and unexposed regions
during development. Following development, the surface of the
semiconductor substrate can be selectively etched by using the
photoresist pattern described above as a mask.
[0008] During exposure of the resist to energy, as described above,
there is a tendency for the acid that effects deprotection to
diffuse from the exposed resist into the unexposed resist. Such
diffusion, if significant enough, will erode the resolution of the
patterned features. The result is features that do not have the
desired dimensions being transferred to the wafer. When the
diffusion is extreme, the latent image in the resist can be
destroyed.
[0009] Accordingly, it is desirable to provide a method for
enhancing resolution of a chemically amplified photoresist. In
addition, it is desirable to provide a method for generating on a
substrate a resist image having well-defined dimensions.
Furthermore, other desirable features and characteristics of the
present invention will become apparent from the subsequent detailed
description of the invention and the appended claims, taken in
conjunction with the accompanying drawings and this background of
the invention.
BRIEF SUMMARY OF THE INVENTION
[0010] In an exemplary embodiment of the invention, a method for
enhancing resolution of a chemically amplified photoresist is
provided. The method comprises depositing on a substrate a film
comprising a photoacid generator and a polymer comprising
functional groups bonded to protecting moieties. The film is
exposed to patterned radiation. The patterned radiation results in
protonation of a portion of the functional groups and the formation
of a latent image within the film. The bonds between the protonated
functional groups and the protecting moieties then are selectively
excited with non-thermal energy having a wavelength spectrum that
resonantly cleaves the bonds.
[0011] In another exemplary embodiment of the invention, a method
for generating a resist image on a substrate is provided. The
method comprises coating a substrate with a chemically amplified
photoresist comprising a photoacid generator and a polymer having
functional groups bonded to acid labile groups. Acid from the
photoacid generator is generated and protonation of a portion of
the functional groups of the polymer is effected. The chemically
amplified photoresist is exposed to electromagnetic radiation
having a wavelength spectrum that is narrower than that of black
body radiation and that corresponds to the absorption spectrum of
the bonds between the protonated functional groups and the acid
labile groups.
[0012] In a further exemplary embodiment of the invention, a method
for device fabrication is provided. The method comprises forming a
layer of chemically amplified photoresist on a substrate. The
chemically amplified photoresist comprises a photoacid generator
and a polymer having bonds between functional groups and protection
groups. The layer of chemically amplified photoresist is exposed to
patterned radiation selected from the group consisting of
ultraviolet radiation, EUV radiation, x-ray radiation, electron
beam radiation, and ion beam radiation to introduce an image into
the photoresist and protonation of the functional groups is
effected. The layer of chemically amplified photoresist is
subjected to electromagnetic radiation that has a wavelength
spectrum that corresponds to the absorption spectrum of the bonds
such that the protection groups are disassociated from the
protonated functional groups. The image is developed into a pattern
and the pattern is transferred into the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The present invention will hereinafter be described in
conjunction with the following drawing figures, wherein like
numerals denote like elements, and wherein:
[0014] FIG. 1 is a flowchart of a method for enhancing resolution
of a chemically amplified photoresist in accordance with an
exemplary embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0015] The following detailed description of the invention is
merely exemplary in nature and is not intended to limit the
invention or the application and uses of the invention.
Furthermore, there is no intention to be bound by any theory
presented in the preceding background of the invention or the
following detailed description of the invention.
[0016] Referring to FIG. 1, a method 100 for enhancing the
resolution of a chemically amplified photoresist in accordance with
an exemplary embodiment of the present invention begins by
depositing on a substrate a film comprising a chemically amplified
photoresist formed of a photoacid generator or "PAG" and a polymer
comprising functional groups bonded to protecting moieties (step
102). The film further comprises a solvent within which the
chemically amplified photoresist is incorporated. The term
"photoresist" is used interchangeably herein with the term
"resist." Photoresists of the present invention may be negative (or
negative-tone) photoresists, or positive (or positive-tone)
photoresists, as these terms are known in the art. Upon exposure of
the chemically amplified photoresist to radiation, one photon or
energetic particle is absorbed by the PAG, which generates an acid
molecule that subsequently may cause or catalyze numerous chemical
events, or may cause or catalyze individual cleavage reactions of
protecting moieties in the chemically amplified photoresist. The
acidic molecules may be considered catalysts because the acid may
be regenerated after each of many individual reactions.
[0017] Suitable substrates upon which the film is deposited include
silicon wafers, either in their original state or upon which
various metal, dielectric or other material layers have been
deposited. The substrate may be functionalized glass, silicon,
germanium, gallium arsenide, gallium phosphorous, silicon dioxide,
silicon nitride, modified silicon or any one of a wide variety of
gels or polymers, such as (poly)tetrafluoroethylene,
(poly)vinylidenedifluoride, polystyrene, polycarbonate,
polypropylene, or combinations thereof. Preferably the surface of
the substrate is cleaned by standard procedures, such as vapor
priming, before the film is disposed thereon. The film can be
coated on the substrate using known techniques, such as spin or
spray coating, dipping, or the like.
[0018] Solvents that can be used for the resist include
methoxypropyl acetate, cyclopentanone, cyclohexanone,
y-butyrolactone, ethyl lactate, diethylene glycol, diethyl ether,
ethylene glycol dimethyl ether, dimethyl ether, or a mixture of at
least two of these solvents. In general, however, the resist
components can be dissolved in any common solvent or mixture
thereof that can form a clear, homogeneous, and storage-stable
solution and that can ensure good coat quality when the substrate
is coated.
[0019] Suitable chemically amplified photoresists include those
chemically amplified photoresists used in DUV, 193 nm, and 157 nm
applications or the like. This includes, but is not limited to,
novolaks, polyvinylphenols, acetals, acrylates, cyclic olefins, and
the like. Other chemically amplified photoresist formulations will
be apparent to those skilled in the art. Chemically amplified
photoresists are commercially available from a number of sources
including Rohm and Haas Electronic Materials of Marlborough, Mass.,
and Tokyo Ohka Kogyo of Tokyo, Japan.
[0020] The base polymer of the chemically amplified photoresist
generally comprises functional groups, such as alcohol (OH), phenol
(C.sub.2H.sub.5OH), carboxylic acid (COOH) and the like, which are
bonded to or "masked" by protective groups, that is, the hydrogen
atom is removed from the functional group and replaced with the
protective group. The protective groups can undergo acidolysis that
results in a significant change in the solubility of the polymer in
developer solution. The polymer typically is a polymer or copolymer
of vinyl phenol and optionally other copolymerizable groups. The
polymers useful in the method of the present invention are not
limited to polymers that are formed by vinylic addition
polymerization, however. Other polymerizations such as
condensation, polyaddition, and addition condensation are useful
mechanisms for producing suitable polymers. Copolymers comprise
units of substituted or unsubstituted phenols and non-aromatic
groups, particularly copolymers of vinyl phenols and alkyl
acrylates, typically alkyl acrylates having from 1 to about 12
carbon atoms. For example, the polymer may include at least one of
poly(p-tertbutoxycarbonyloxy-.alpha.a-methylstyrene),
poly(p-tert-butoxycarbonyloxystyrene), poly(tert-butyl
p-vinylbenzoate), poly(tert-butyl p-isopropenylphenyloxyacetate),
poly(tert-butyl methacrylate), polymethylmethacrylate,
acrylate-based polymers, a novolak/diazonaphthoquinione resin, a
nitrene-crossed hydroxystyrene polymer, and poly(butene-1-sulfone).
For convenience, "tert" is shortened to "t" hereinafter. In another
example, the polymer comprises phenolic and cyclic alcohol units,
hydroxystyrene and acrylate, methacrylate, mixtures of acrylate and
methacrylate, adamantyl methacrylate, 3-oxo-cyclohexyl
methacrylate, tetrahydropyranymethacrylate, trycyclodecanyl
acrylate, isobornyl polymers, polynorbornene,
polyanthrylmethacrylate, poly(vinylmethyl ether-co-maleic
anhydride), or poly(styrene-co-maleic anhydride). The polymeric
material may include a partially t-butoxycarbonyloxy-substituted
poly-p-hydroxystyrene, partially t-butoxycarbonyloxy-substituted
poly-3-hydroxyphenyl phenylsiloxane, partially t-butyl-substituted
polymethacrylate, and partially adamantly-substituted
polymethacrylate.
[0021] Examples of suitable protecting moieties include acid labile
groups such as acetal groups, ketal groups,
beta-silicon-substituted alkyls such as
bis(trimethylsilylmethyl)methyl and 1-(trimethylsilylmethyl)methyl,
tert-butyl esters, tert-butyl esters of carboxylic acids, and
tert-butyl ethers. It is understood that a wide range of acid
labile groups are operative in the invention.
[0022] Examples of suitable polymers with these acid labile groups
include acrylate-based polymers and copolymers, methacrylate-based
polymers and copolymers, copolymers with alicyclic moieties (e.g.
norbornene) either incorporated into the polymer backbone or
pendant to the polymer backbone. Examples of these polymers include
tetra polymers such as poly(cycloolefin-alt-maleic
anhydride-co-t-butyl acrylate-co-acrylic acid) wherein the
cycloolefin is, for example, norbornene,
5,6-dihydrodicyclopentadiene, 1,5-cyclooctadiene, and
1,5-dimethyl-1,5-cyclooctadiene.
[0023] Photoacid generators useful in the practice of the present
invention include, without limitation, metallic, metalloid, and
non-metallic onium salts, aryl sulfonates including, without
limitation, tris-pyrogallol sulfonates and anthracene-2-sulfonates
such as 9,10-diethylanthracene-2-sulfonate, 2-nitrobenzyl esters,
beta-ketosulfones, disulfones, arylsulfonyl-alpha-keto- and alpha
carboxyl-diazomethanes, and precursors of substituted and
unsubstituted sulfonic acids.
[0024] Additional examples of photoacid generators useful in the
practice of the present invention include
N-(trifluoromethylsulfonyloxy)-bicyclo-[2.2.1]hept-5-ene-2,3-dicarboximid-
e (MDT), N-(trifluoromethylsulfonyloxy) nitronaphthalimides,
N-(trifluoromethylsulfonyloxy)-4-halonaphthalimides,
N,N'-bis(camphorsulfonyloxy)-3,4,9,10-perylenetetracarbox-diimide,
N-(trifluoromethylsulfonyloxy)-7-oxabicyclo-[2.2.1]hept-5-ene-2,3-dicarbo-
ximide, N-(trifluoromethylsulfonyloxy)-succinimide,
N,N'-bis(trifluoromethylsulfonyloxy)-(3-methyl-4,5-imido-cyclohex-3-pheny-
l)-succinimide, N-(trifluoromethylsulfonyloxy)-diphenylmaleimide,
di-[N-(trifluoromethylsulfonyloxy)-phthalimidyl]ether,
bistrifluoromethyl-bis-N,N-(trifluoromethylsuflonyloxy)-phthalimidylmetha-
ne, N-(camphorsulfonyloxy)-naphthalimide,
N-(camphorsulfonyloxy)-nitronaphthalimides, and the corresponding
tosyl-, brosyl-, fluoro-, and perfluoro-benzenesulfonyloxy-,
nitrobenzenesulfonyloxy-, and halobenzenesulfonyloxy-analogs
thereof. It will be understood that other photoacid generators
known in the art may also be useful in the practice of the present
invention.
[0025] The photoacid generator will be selected to respond to the
light energy used for pattern-wise exposing the chemically
amplified photoresist. Photoacid generators are currently available
for a variety of different wavelengths from visible to X-ray;
accordingly, the artisan will select the appropriate photoacid
generator based on their knowledge of the kind of radiation to
which the photoresist will be exposed during patterned radiation.
The photoacid generator will preferably comprise about 0.01 to
about 20% by weight of the photoresist composition, more preferably
about 1 to about 10% by weight.
[0026] In an optional exemplary embodiment of the invention, after
the chemically amplified photoresist is deposited onto the
substrate, the film may be heated or "soft-baked" to improve
adhesion of the photoresist to the substrate and to evaporate the
solvent in which the photoresist is dispersed (step 104). In an
exemplary embodiment of the invention, the film is heated to a
temperature in the range of about 70 to 150.degree. C. In another
exemplary embodiment of the invention, the film is heated for a
period of about 30 to 60 seconds. After heating, the film then is
allowed to cool.
[0027] As mentioned above, the film is exposed to patterned
radiation (step 106). The radiation may comprise any radiation
commonly used to create a latent image in chemically amplified
photoresist, such as patterned x-ray radiation, patterned e-beam
radiation, patterned ion beam radiation, patterned extreme
ultraviolet (EUV) radiation, patterned ultraviolet radiation, or
the like. Preferably, the film is exposed to ultraviolet radiation
with a wavelength in the range of about 13 nm to about 370 nm and
more preferably, to ultraviolet radiation at a wavelength of about
193 nm or 13.5 nm. The radiation is absorbed by the
radiation-sensitive acid generator to generate free acid. The free
acid results in protonation of the functional group of the
chemically amplified photoresist. In addition, the radiation
creates in the photoresist a latent image of the pattern of the
radiation, which image is to be transferred to the substrate.
[0028] After the film is exposed to patterned radiation, the bonds
between the protonated functional groups and the protecting
moieties, e.g., the acid labile groups, are selectively excited
(step 108). The bonds are selectively excited by exposing the film
to a non-thermal source of energy that has a relatively narrow
wavelength spectrum that is less than that of black body radiation
and that corresponds to the absorption spectrum of the bonds. In
this manner, the non-thermal energy resonantly cleaves the bonds,
thus resulting in disassociation of the protecting moieties from
the protonated functional groups. As noted above, the portion of
the photoresist having fewer bonded protecting moieties has a much
different solubility when exposed to a developer than the portion
of the photoresist having more bonded protecting moieties. By using
a non-thermal source of energy with a narrow wavelength spectrum,
the deprotection reaction is facilitated while generation of heat
is reduced or minimized. By reducing or minimizing heat generation,
diffusion of the acid from radiated areas of the film to
non-radiated areas of the film, which otherwise would be enhanced
by heat generation, is minimized. This reduction in acid diffusion
results in enhanced resolution of the photoresist.
[0029] Suitable types of non-thermal energy that may be used to
excite the bonds between the protonated functional groups and the
protecting moieties include infrared radiation, preferably infrared
radiation having a wavelength greater than about 10,000 nm,
radiation having a wavenumber of 1750 cm.sup.-1, radiation having a
wavenumber of 1180 cm.sup.-1, microwave radiation, and the like.
Sources of non-thermal energy that can provide a narrow wavelength
spectrum suitable for use in the present invention include lasers
and sources of THz radiation. The photoresist is exposed to the
non-thermal energy source for a time sufficient to permit the free
acid and the non-thermal energy to cleave the bonds. In a preferred
embodiment, the photoresist is exposed to the non-thermal energy
source for a time sufficient to permit the free acid and the
non-thermal energy to cleave the bonds and to regenerate the acid.
More preferably, the photoresist is exposed to the non-thermal
energy source for about 2 seconds up to about 5 minutes. In one
exemplary embodiment of the invention, the photoresist film is
exposed to the non-thermal energy source continuously during this
time range. In another exemplary embodiment of the invention, the
photoresist film is exposed to pulses of the non-thermal energy
during this time range. In this manner, the total heat absorbed by
the resist film during the exposure to the non-thermal energy
source can be further reduced because the bonds between the
protonated functional groups and the protecting moieties can be
cleaved during the heat pulses and the acids can reprotonate
another protecting moiety between the heat pulses (in the "off"
time of the cycle), thus producing the desired chemical
amplification with minimal diffusion.
[0030] In an optional embodiment of the invention, before, during
or after the photoresist is exposed to the non-thermal energy
source, a small amount of heat is applied to the photoresist (step
110). The amount of heat applied to the photoresist is less than
that which would be applied to the photoresist during a
post-patterned radiation bake to facilitate the deprotection
reaction by the acid. In this manner, diffusion of the acid can be
better controlled so that a sufficient amount of acid is permitted
to diffuse through the area of the photoresist that was exposed to
the patterned radiation to enhance the deprotection reaction, while
diffusion of the acid to and through the areas of the photoresist
that were not so exposed is reduced or minimized. Alternatively,
while the photoresist is exposed to the non-thermal energy source,
it can be cooled, thereby further reducing or minimizing the
diffusion of the acid to and through the areas of the photoresist
that were not exposed to the patterned radiation.
[0031] After the non-thermal energy exposure, the latent image in
the photoresist then is developed using a suitable solvent (step
112). Suitable solvents for developing the image include an aqueous
base, preferably an aqueous base without metal ions, such as the
industry standard developer tetramethyl ammonium hydroxide or
choline, or water and base with lower alkyl alcohols such as
isopropanol, ethanol, methanol, and mixtures thereof. Generally,
immersion in the developer for a time period from about 10 seconds
to about 5 minutes produces the desired delineation. After the
development, the wafer is dried and cooled and the pattern in the
resist then is transferred into the underlying substrate using
conventional etching expedients well known to one skilled in the
art.
[0032] Accordingly, a method for enhancing the resolution of a
chemically amplified photoresist has been described. The method
permits facilitation of the deprotection reaction, while reducing
or controlling acid diffusion that otherwise could compromise the
integrity of the image to be transferred by the photoresist. While
at least one exemplary embodiment has been presented in the
foregoing detailed description of the invention, it should be
appreciated that a vast number of variations exist. It should also
be appreciated that the exemplary embodiment or exemplary
embodiments are only examples, and are not intended to limit the
scope, applicability, or configuration of the invention in any way.
Rather, the foregoing detailed description will provide those
skilled in the art with a convenient road map for implementing an
exemplary embodiment of the invention, it being understood that
various changes may be made in the function and arrangement of
elements described in an exemplary embodiment without departing
from the scope of the invention as set forth in the appended claims
and their legal equivalents.
* * * * *